The present invention relates generally to bolted composite joints and, more particularly, to a conical metal load spreader between a bolt head and a composite aircraft gas turbine fan platform.
An aircraft turbofan gas turbine engine includes a fan assembly having a plurality of circumferentially spaced apart fan blades extending radially outwardly from a rotor disk. The fan assembly typically includes a plurality of circumferentially spaced apart fan blades each having a dovetail root disposed in a complementary, axially extending dovetail groove or slot in a perimeter or rim of a rotor disk. A spinner is mounted to a front end of the fan assembly to provide smooth airflow into the fan. A radially inner flowpath boundary for the airflow channeled between the blades is provided typically by integral or non-integral platforms at the blade roots which circumferentially abut each other between adjacent fan blades.
There are often reasons for increasing the airflow through the fan blades to increase overall engine performance without increasing or holding to a limit of a tip of the fan blade. An inner flowpath boundary, often referred to as the hub, is moved radially inwardly from an existing engine design or the engine is originally designed to have, what is referred to as, a low radius hub. Low radius hubs present assembly challenges between the platforms and disk as the inner flowpath boundary tends to meet tops of disk dovetail posts at a forward end of the disk, thus, limiting the space for platform interface and mounting features.
United States Patent Application No. 2014/0186187 by Jorge Orlando Lamboy et al., published Jul. 3, 2014, entitled “NON-INTEGRAL FAN BLADE PLATFORM” and assigned to the present assignee, the General Electric Company discloses a blade platform for a low hub radius fan. The fan platform between adjacent blades is secured by mounting features to the disk. The fan platform is secured to the rotor structure or disk with lugs or overlaps with support rings. It is desirable to have a composite platform. It is also desirable to locate the forward radius of the hub air flow surface radially inward as far as mechanically feasible. This increases fan flow area and allows for improved overall engine performance. The platform design and forward radius have been limited to a certain size for past engines by the mechanical attachment of the fan platform to the fan rotor.
There remains a need for an improved mechanical attachment assembly to secure or mount a fan composite platform to a metal disk that permits a low radius hub design.